1. Field
The disclosed subject matter relates to a light emitting semiconductor apparatus and more particularly to a light emitting semiconductor apparatus containing a plurality of light emitting semiconductor devices.
2. Description of the Related Art
A light emitting semiconductor device (hereinafter abbreviated as “light emitting device”) has a small external size with a small emission amount of light, and accordingly has an optical property nearing that of a point light source. Typical light emitting semiconductor apparatus that include a light emitting device as a light emitting source are assembled, for example, in LCD back-lights, reading light sources for printers, panel illuminators, general illuminators, various indicators, etc. In such cases, a plurality of light emitting devices having almost equal light emission spectral distributions and direction characteristics are mounted to ensure a required (or desired) amount of illuminating light. The “direction characteristic” is defined as “a series of relative values of brightness measured at different angles to the optical axis of a light emitting semiconductor device and graphed with a continuous line”.
In a further proposed light emitting semiconductor apparatus, a light emitting device is sealed in a light transmissive resin containing one or more wavelength conversion materials, such as phosphors. In this case, a light emitted from the light emitting device is used to excite the phosphor for wavelength conversion and release a light different in chromaticity from the light emitted from the light emitting device.
For example, if the light emitted from the light emitting device is a blue light, the apparatus may use a phosphor that can wavelength-convert the blue light into a complementary color of blue (e.g., a yellow light) when excited by the blue light. In this case, the yellow light that was wavelength-converted when part of the blue light emitted from the light emitting device excited the phosphor and the blue light that was emitted directly from the light emitting device are subjected to additional color mixture to obtain a light chromatically near a white light.
Similarly, if the light emitted from the light emitting device is a blue light, the apparatus may use two types of phosphors in mixture that can wavelength-convert the blue light into a green and a red light when excited by the blue light. In this case, the green and red lights (that result from the wavelength-conversion when part of the blue light emitted from the light emitting device excites the phosphors) and the blue light emitted directly from the light emitting device are subjected to additional color mixture to obtain a light chromatically almost equal to a white light.
In addition, if the light emitted from the light emitting device is an ultraviolet light, the apparatus may use three types of phosphors in mixture that can wavelength-convert the ultraviolet light into a blue, a green and a red light when excited by the ultraviolet light. In this case, the blue, green and red lights (that result from the wavelength-conversion when part of the ultraviolet light emitted from the light emitting device excites the phosphors) are subjected to additional color mixture to obtain a light chromatically almost equal to a white light.
Further, the types of light emitted from the light emitting device and the types of phosphor may be mixed appropriately to obtain various chromatic lights, such as a light almost equal to a white light or a light other than the light chromatically near the white light. For example, Japanese Patent Publication No. JP 2005-285874A and its English translation/equivalent which are hereby incorporated in their entireties by reference disclose such a light emitting device.
Even if the light emitting devices have the same semiconductor material and structure, that is, the same light emission spectral distribution, different external shapes and sizes of the light emitting devices can vary the direction characteristics of light emitted from the light emitting devices. Furthermore, if the external shapes and sizes are identical, different shapes and sizes of the electrodes can also vary the direction characteristics. In particular, an electrode located on a light exit surface of the light emitting device greatly affects the characteristics thereof.
For example, the following three types of different light emitting devices are assumed to have the same material and structure (the same light emission spectral distribution) and almost the same size with differences only in external form. A light emitting device A is in the form of an almost cube, as shown in FIG. 1. A light emitting device B is in the form of an almost truncated quadrangular pyramid, as shown in FIG. 2. A light emitting device C is in the form of an almost truncated reverse quadrangular pyramid, as shown in FIG. 3. They have respective direction characteristic, which are graphed in curved forms as shown in FIG. 4 for the light emitting device A, FIG. 5 for the light emitting device B, and FIG. 6 for the light emitting device C. These figures show curves that represent the intensity of light (luminous intensity: cd) in polar coordinates (distribution curves of luminous intensity), which indicate how intense and in which direction the light can be emitted from the light emitting devices A, B, C. A light distribution is fundamentally determined by measuring the intensity of light across the whole cross section although it is represented by luminous intensities in a single cross section because luminous intensities in different cross sections are almost identical. The external graph forms of the direction characteristics are expressed as follows. Namely, the light emitting device A has an almost spherical form as shown in FIG. 4, the light emitting device B has an almost reverse conical form as shown in FIG. 5, and the light emitting device C has an almost conical form as shown in FIG. 6.
A plurality of light emitting devices with almost equal light emission spectral distributions and direction characteristics can be mounted and sealed in a sealing resin composed of a light transmissive resin containing one or more phosphors to configure a light emitting semiconductor apparatus. A conventionally proposed example of such apparatus has an arrangement shown in FIGS. 14 and 15. FIG. 14 is a front view, and FIG. 15 is a cross-sectional view taken along line A-A of FIG. 14.
The apparatus shown in FIGS. 14 and 15 includes a resin molding body 51 (hereinafter referred to as “lamp house 51”) formed as a package obtained by insert molding a lead frame 50 in resin and forming a recess 53 therein having an aperture 52. The recess 53 has an inner bottom, through which four bonding pads 54 are exposed in line on respective ends of four separate lead frames 50. Among those, the outermost bonding pads 54 in a pair extend through the lamp house 51 and lead out of the outer circumferential surface of the lamp house 51 to an area external to the device. A pair of external connection terminals 55 on the other end of the lead frames 50 are located along the outer circumferential surface of the lamp house 51.
Light emitting devices C of FIG. 3 (reference 56 in FIG. 15) are die-bonded via a conductive bonding member to the three bonding pads 54 that are exposed through the inner bottom of the recess 53, respectively. The light emitting device 56 has a lower electrode electrically conducted to the bonding pad 54 on which the light emitting device 56 is mounted.
On the other hand, an upper electrode on the light emitting device 56 and a bonding pad 54 adjacent to the bonding pad 54 on which the light emitting device 56 is mounted are wire-bonded to each other via a bonding wire 57 to establish electrical conduction therebetween.
Further, the recess 53 is filled with a sealing resin 58 composed of a light transmissive resin containing one or more phosphors to seal the light emitting devices 56 and the bonding wires 57 in resin.
Another conventional art device includes a light emitting semiconductor apparatus as shown in FIGS. 16 and 17. FIG. 16 is a front view, and FIG. 17 is a cross-sectional view taken along line A-A of FIG. 16. In this light emitting semiconductor apparatus, the light emitting devices B of FIG. 2 (light emitting device 59 of FIG. 15) are mounted instead of the light emitting devices C of FIG. 3, thus differentiating the device of FIGS. 16 and 17 from the above-described light emitting semiconductor apparatus of FIGS. 14 and 15.
In either one of the light emitting semiconductor apparatus of the conventional/related art, the light emitting devices 56, 59 are electrically connected in series. When a voltage is applied across a pair of the external connection terminals 55 that are led out of the lamp house 51 and located along the outer circumferential surface of the lamp house 51, all the light emitting devices 56, 59 are driven to emit light.
The light emitting device C has the direction characteristic shown in FIG. 6 and the light emitting device B has the direction characteristic shown in FIG. 5. The two types of light emitting semiconductor apparatus of the conventional/related art which contain such light emitting devices also have the direction characteristics shown in FIGS. 15 and 17, respectively.
The direction characteristics of the light emitting semiconductor apparatus of FIG. 15 which contains the plurality of light emitting devices C includes a region between adjacent light emitting devices C where light distributions thereof overlap widely, as shown. The presence of such a light distribution overlap region causes the following problem when incorporated into a light emitting semiconductor apparatus.
First, the overlap region receives a larger amount of light emitted from the light emitting device C than other regions such as a region in the vicinity of the optical axis of the light emitting device C. The overlap region also receives a larger amount of light that is wavelength-converted by the phosphor contained in the sealing resin and covering the light emitting device C, in comparison with other regions.
For example, if it is assumed that the light emitted from the light emitting device C is a blue light, and the apparatus uses a phosphor that can wavelength-convert the blue light into a complementary color yellow light when excited by the blue light to obtain a light chromatically near a white light, then when the light emitting semiconductor apparatus is observed from the direction of illumination, a bluish white light is released from an area where the light emitting device C is located. This is because the area has a stronger light source color received from the light emitting device C. A yellowish white light is released from an area between the light emitting devices C because the area has a stronger wavelength-converted light. As a result, the light emitting semiconductor apparatus exhibits color unevenness.
The phosphor and the light transmissive resin contained in the sealing resin, which are topically irradiated with the blue light having relatively higher energy among the various light rays, will deteriorate faster than the light transmissive resin and the phosphor in other regions.
Therefore, the deterioration of the light transmissive resin over time causes a reduction in the transmissivity of the resin and a variation in color. Similarly, the deterioration of the phosphor over time causes a reduction in the wavelength conversion efficiency of the phosphor. As a result, in the light emitting semiconductor apparatus, various problems arise over time associated with the topical deterioration and with respect to the amount and chromaticity of the illuminating light.
Specifically, a difference in topical deterioration rate between the phosphor and the light transmissive resin contained in the sealing resin results in remarkable variations in brightness and chromaticity in accordance with the cumulative drive time for the light emitting semiconductor apparatus.
On the other hand, the direction characteristic of the light emitting semiconductor apparatus of FIG. 17 which includes light emitting devices B also includes a region between adjacent light emitting devices B where light distributions thereof widely overlap, as shown.
Further, there is also a region that receives a smaller amount of light from the light emitting device B, as shown. This region becomes a factor that causes a variation in color of the light emitting semiconductor apparatus because only a small amount of light can be wavelength-converted by the phosphor at this location.
Therefore, various problems arise associated with the variation in color of the illuminating light as well as from the topical deterioration over time of the amount and chromaticity of the illuminating light, similar to the problems described above with respect to the device of FIG. 15.